The present invention relates to a torque sensor suitable for use in a power steering device.
FIGS. 9 to 12 show a construction of a torque sensor 100 of a conventional art (shown in Patent Document 1, for example). FIG. 9 is a perspective view in the vicinity of the torque sensor. FIG. 10 is a partially enlarged view of FIG. 9. FIGS. 11 and 12 are diagrams for explaining the action.
[Patent Document 1] Patent No. 3094049
In FIG. 9, the torque sensor 100 is provided between a first shaft 101 and a second shaft 102. At the first shaft 101, a magnetism generation portion 103 for outputting a magnetic flux is provided. The magnetism generation portion 103 has a plurality of magnets 104 provided in the circumferential direction around the first shaft 101. The magnets 104 are magnetized toward the axis core direction (arrow direction) of the first shaft 101 and the adjoining magnets 104 are magnetized in the direction opposite to each other, and thus, when the magnetism generation portion 103 is seen from the second shaft 102 side, as shown in FIG. 10, magnetic poles different from each other are adjoined. That is, S poles and N poles are arranged alternately.
As shown in FIG. 9, the second shaft 102 is provided with an outer ring 105 and an inner ring 106, and as shown in FIG. 10, a plurality of outer magnetic path pieces 107 are extended from the outer ring 105, while inner magnetic path pieces 108 are extended from the inner ring 106. As shown in FIG. 10, a clearance 109 is provided between the outer ring 105 and the inner ring 106, and a magnetic sensor 110 is arranged in the clearance 109.
Next, action will be described. Suppose that a driver does not steer a steering wheel. In this case, since the first shaft 101 is not rotated with respect to the second shaft 102, as shown in FIG. 11, each outer magnetic path piece 107 is opposed to the N pole and the S pole of the magnet 104 over the same area each, and each inner magnetic path piece 108 is similarly opposed to the N pole and the S pole of the magnet 104 over the same area each. In this case, the magnetic flux is not guided to the outer magnetic path piece 107 and the inner magnetic path piece 108, and the magnetic flux outputted from the N pole of the magnet 104 is inputted to the S pole of the magnet 104. Therefore, the magnetic flux sensor 110 does not detect the magnetic flux.
Next, suppose that the driver has steered the steering wheel. In this case, the first shaft 101 is rotated with respect to the second shaft 102, and as shown in FIG. 12, the outer magnetic path piece 107 is moved to the S pole side, while the inner magnetic path piece 108 is moved to the N pole side. In this case, since the magnetic flux outputted from the N pole of the magnet 104 reaches the S pole of the magnet 104 via the inner magnetic path piece 108, the inner ring 106, the magnetic sensor 110, the outer ring 105, and the outer magnetic path piece 107, a rotation amount of the first shaft 101 with respect to the second shaft 102, that is, a steering torque of the steering wheel can be detected based on the magnetic flux amount detected by the magnetic sensor 110.
In the above-mentioned background art, since the torque sensor 100 is in the structure that it is provided between the first shaft 101 and the second shaft 102 in the axial direction, the entire length is long in the axial direction due to a space in which the torque sensor 100 is arranged. Thus, the torque sensor 100 which can be accommodated in the compact manner in the axial direction has been in demand.
The present invention was made in view of the problems of the background art and has an object to provide a torque sensor which can reduce the length in the axial direction when it is attached to two shafts whose torque is to be detected.